Light source apparatus, optical apparatus, exposure apparatus, device manufacturing method, illuminating method, exposure method, and method for manufacturing optical apparatus

ABSTRACT

An optical apparatus, which illuminates a first area with light from a light source while the first area is longer in a second direction intersecting a first direction than in the first direction, includes a collector optical member which is arranged in an optical path between the light source and the first area, and condenses the light from the light source to form a second area in a predetermined plane, the second area being longer in a fourth direction intersecting a third direction than in the third direction; and a first fly&#39;s eye optical member which is provided within the predetermined plane including the second area, and has a plurality of first optical elements guiding the light of the collector optical member to the first area.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/623,749, filed on Jun. 15, 2017, which is a continuation of U.S.application Ser. No. 13/639,037, filed on Dec. 17, 2012, which is a U.S.national phase entry of International Application No. PCT/JP2011/058189,filed on Mar. 31, 2011, which claims the conventional priority of U.S.Provisional Patent Applications No. 61/320,453, filed on Apr. 2, 2010and No. 61/320,443, filed on Apr. 2, 2010 and the disclosures of whichare incorporated herein by reference in their entirety.

BACKGROUND 1. Field

The present teaching relates to a light source apparatus, an opticalapparatus, an exposure apparatus, a device producing method, anillumination method, an exposure method, and an optical apparatusproducing method. More specifically, the present teaching relates to anillumination optical system of an exposure apparatus which is used toproduce devices such as semiconductor elements, imaging elements, liquidcrystal display devices, thin-film magnetic heads, etc., through alithography process.

2. Description of the Related Art

Conventionally, in an exposure apparatus which is used to producesemiconductor elements, etc., a circuit pattern formed on a mask(reticle) is projected and transferred onto a photosensitive substrate(for example, a wafer) via a projection optical system. A resist coatedon the photosensitive substrate is exposed through projection exposurevia the projection optical system, and thus a pattern of the resist(resist pattern) corresponding to a pattern of the mask (mask pattern)is obtained. The resolving power (resolution) of the exposure apparatusdepends on the wavelength of an exposure light (exposure light beam) andthe numerical aperture of the projection optical system. Therefore, inorder to improve the resolving power of the exposure apparatus, it isrequired to shorten the wavelength of the exposure light and to increasethe numerical aperture of the projection optical system.

From the viewpoint of optical design, it is generally difficult toincrease the numerical aperture of the projection optical system to apredetermined value or more. Therefore, it is necessary to shorten thewavelength of the exposure light. In view of this, attention is directedto an EUVL (Extreme UltraViolet Lithography) technique, which uses anEUV light (Extreme UltraViolet light or light beam) having a wavelengthof approximately 5 nm to 20 nm, as a next-generation exposure technique(exposure apparatus) to be used for patterning semiconductor elements.In the case of using the EUV light as the exposure light, any usablelight-transmissive optical material is not available. Therefore, the EUVexposure apparatus uses a reflection-type optical integrator, areflection-type mask, and a reflection-type projection optical system.

For an ordinary exposure apparatus not limited to the EUV exposureapparatus, it is desirable to uniformize the light intensitydistribution formed in a pupil of the illumination optical system (alsoreferred to as “pupil intensity distribution” hereinbelow). The presentapplicant proposes a technique of forming an almost uniform pupilintensity distribution in an illumination pupil by elaborating thecorresponding relation between a plurality of first mirror elements in afirst fly's eye optical member and a plurality of second mirror elementsin a second fly's eye optical member in the reflection-type opticalintegrator (see, United States Patent Application Publication No.2007/0273859).

SUMMARY

In the illumination optical system disclosed in U.S. Patent ApplicationPublication No. 2007/0273859, the respective light fluxeswavefront-divided by the plurality of first mirror elements in the firstfly's eye optical member form, in a superposed manner, an illuminationarea as an image of the first mirror elements on a pattern surface ofthe mask which is the irradiation surface (surface to be irradiated),via the corresponding second mirror elements in the second fly's eyeoptical member. However, as will be described hereinafter, a distortionmay arise from the relative disposition and the like between the firstfly's eye optical member and the second fly's eye optical member, andtherefore the image of the first mirror elements formed on theirradiation surface does not take a similar shape to the first mirrorelements. As a result, the plurality of light fluxes wavefront-dividedby the plurality of first mirror elements form the respectiveilluminating fields on the irradiation surface off the superposedillumination area of a desired profile (outer shape), and consequently alight loss arises from a so-called overlap error of the illuminatingfields.

The present teaching has been made taking the foregoing problem intoconsideration, an object of which is to illuminate the irradiationsurface under a required illumination condition capable of achieving ahigh light efficiency while keeping the light loss small.

According to a first aspect of the present teaching, there is providedan optical apparatus illuminating a first area with light from a lightsource, the first area being longer in a second direction intersecting afirst direction than in the first direction, the optical apparatusincluding: a collector optical member which is arranged in an opticalpath between the light source and the first area, and condenses thelight from the light source to form a second area in a predeterminedplane, the second area being longer in a fourth direction intersecting athird direction than in the third direction; and a first fly's eyeoptical member which is provided within the predetermined planeincluding the second area, and has a plurality of first optical elementsguiding the light from the collector optical member to the first area.

According to a second aspect of the present teaching, there is providedan optical apparatus used for illuminating a first area with light froma light source, the first area being longer in a second directionintersecting a first direction than in the first direction, the opticalapparatus including: a first fly's eye optical member which is providedin an optical path between the light source and the first area, andwhich includes a plurality of first optical elements aligned in apredetermined plane, the plurality of first optical elements each havinga profile longer in a fourth direction intersecting a third directionthan in the third direction, the plurality of first optical elementsforming an aggregate having length in the third direction and in thefourth direction which are different from each other; and a second fly'seye optical member which is provided in an optical path between thefirst fly's eye optical member and the first area, and has a pluralityof second optical elements arranged to correspond optically to the firstoptical elements.

According to a third aspect of the present teaching, there is providedan optical apparatus used for illuminating a first area with light froma light source, the first area being longer in a second directionintersecting a first direction than in the first direction, the opticalapparatus comprising: a first fly's eye optical member which is providedwithin a predetermined plane including a second area, and has aplurality of first optical elements, wherein at least one of theplurality of first optical elements has an optical surface, the opticalsurface having surface curvatures along a third direction and along afourth direction intersecting the third direction, which are differentfrom each other within the surface perpendicular to the second area.

According to a fourth aspect of the present teaching, there is providedan exposure apparatus including the optical apparatus according to thefirst aspect, the second aspect, or the third aspect for illuminating apredetermined pattern formed in the first area, wherein a photosensitivesubstrate is exposed with the predetermined pattern.

According to a fifth aspect of the present teaching, there is provided adevice producing method including the steps of: exposing thephotosensitive substrate with the predetermined pattern by using theexposure apparatus according to the fourth aspect; developing thephotosensitive substrate to which the predetermined pattern has beentransferred to form, on a surface of the photosensitive substrate, amask layer shaped to correspond to the predetermined pattern; andprocessing the surface of the photosensitive substrate via the masklayer.

According to a sixth aspect of the present teaching, there is provided alight source apparatus supplying light to a fly's eye optical memberprovided within a predetermined plane, the apparatus including: alight-emitting portion emitting the light; and a collector opticalmember condensing the light emitted by the light-emitting portion toform, in the predetermined plane, a second area longer in a fourthdirection intersecting a third direction than in the third direction.

According to a seventh aspect of the present teaching, there is providedan illumination method for illuminating a first area with light from alight source, the first area being longer in a second directionintersecting a first direction than in the first direction, the methodincluding the steps of: condensing the light from the light source andguiding the light to a second area on a predetermined plane;wavefront-dividing the light into a plurality of light fluxes having aprofile longer in a fourth direction intersecting a third direction thanin the third direction on the predetermined plane; and guiding theplurality of wavefront-divided light fluxes to the first area, whereinthe second area has a shape longer in the fourth direction than in thethird direction; and the plurality of light fluxes on the predeterminedplane are aligned in a plurality of rows along the third direction andalong the fourth direction.

According to an eighth aspect of the present teaching, there is providedan exposure method including the steps of: illuminating the first areain a predetermined pattern by using the illumination method according tothe seventh aspect; and exposing a photosensitive substrate with thepredetermined pattern.

According to a ninth aspect of the present teaching, there is provided adevice producing method including the steps of: exposing thephotosensitive substrate with the predetermined pattern by using theexposure method according to the eighth aspect; developing thephotosensitive substrate to which the predetermined pattern has beentransferred to form, on a surface of the photosensitive substrate, amask layer shaped to correspond to the predetermined pattern; andprocessing the surface of the photosensitive substrate via the masklayer.

According to a tenth aspect of the present teaching, there is providedan optical apparatus producing method used for illuminating a first areawith light from a light source, the first area being longer in a seconddirection intersecting a first direction than in the first direction,the method including the steps of: obtaining a collector optical membercondensing the light from the light source to form a second area in apredetermined plane, the second area being longer in a fourth directionintersecting a third direction than in the third direction; andarranging a first fly's eye optical member having a plurality of firstoptical elements within the predetermined plane including the secondarea.

According to an eleventh aspect of the present teaching, there isprovided an optical apparatus producing method used for illuminating afirst area with light from a light source, the first area being longerin a second direction intersecting a first direction than in the firstdirection, the method including the steps of: preparing a plurality offirst optical elements having a profile longer in a fourth directionintersecting a third direction than in the third direction; andobtaining a first fly's eye optical member which includes an aggregateof the plurality of first optical elements aligned in the thirddirection and the fourth direction, the aggregate having differentlengths from each other in the third direction and in the fourthdirection.

According to the embodiments as described above, it is possible toilluminate the irradiation surface under a required illuminationcondition capable of achieving a high light efficiency while keeping theoccurrence of light loss at a low level. As a result, it is possible toachieve a high throughput.

FIG. 1 schematically shows a construction of an exposure apparatusaccording to an embodiment of the present teaching;

FIG. 2 is a diagram for schematically explaining one time of scanningexposure according to the embodiment;

FIG. 3 schematically shows a construction of a first fly's eye opticalmember in an optical integrator;

FIG. 4 schematically shows a construction of a second fly's eye opticalmember in the optical integrator;

FIG. 5 is a first diagram schematically showing a construction of acollector optical member according to the embodiment;

FIG. 6 is a second diagram schematically showing the construction of thecollector optical member according to the embodiment;

FIG. 7 schematically shows a construction of an exposure apparatusaccording to a first modification;

FIG. 8 is a first diagram schematically showing a construction of acollector optical member according to the first modification;

FIG. 9 is a second diagram schematically showing the construction of thecollector optical member according to the first modification;

FIG. 10 shows an aspect of an optically corresponding relation betweenfirst mirror elements and second mirror elements;

FIG. 11 shows an aspect of forming a light source image elongated in onedirection in one of the second mirror elements in the first modificationshown in FIG. 7;

FIG. 12 schematically shows an example of a light source image formed inone of the second mirror elements by forming toroidal reflectingsurfaces of the first mirror elements in a second modification;

FIG. 13 schematically shows another example of the light source imageformed in the second mirror element by forming the toroidal reflectingsurfaces of the first mirror elements in the second modification;

FIG. 14 shows an effect obtained by applying the technique of the secondmodification to the construction of the embodiment shown in FIG. 1; and

FIG. 15 shows a flowchart concerning an exemplary technique adopted whena semiconductor device is obtained as a microdevice by way of example.

DESCRIPTION OF EMBODIMENTS

Hereinbelow, an embodiment will be explained based on the accompanyingdrawings. FIG. 1 schematically shows a construction of an exposureapparatus according to the embodiment of the present invention. In FIG.1, the Z axis is defined along the normal direction of a surface(exposure surface) of a wafer W which is a photosensitive substrate, theY axis is defined in the direction parallel to the sheet surface of FIG.1 in the surface of the wafer W, and the X axis is defined in thedirection perpendicular to the sheet surface of FIG. 1 in the surface ofthe wafer W, respectively. Referring to FIG. 1, in the exposureapparatus of the embodiment, exposure light (illumination light) issupplied from a light source apparatus including a light source unit LUof DPP (Discharge Produced Plasma) type, and a collector optical member1.

In the light source unit LU of DPP type, when a voltage is applied tothe electrodes made of a target substance (material), or to theelectrodes between which the target material is present, then dischargewill occur between the electrodes at the point of time when the voltageexceeds a certain value, thereby turning the target material intoplasma. This discharge causes a large (electric) current to flow betweenthe electrodes. Thus, the plasma compresses itself into a miniaturespace due to the magnetic field produced by this current, therebyraising the plasma temperature. From this high-temperature plasma, EUVlight is emitted. A light source supplying (exciting) energy to theplasma through discharge to emit the EUV light, in this manner, isgenerally called a DPP light source.

The EUV light emitted from the light source unit LU comes into acollimator optical member 2 via the collector optical member 1. Thecollector optical member 1 includes a concave-surface reflecting mirror1 a with a through hole formed in the center, and a convex-surfacereflecting mirror 1 b with a through hole formed likewise in the center,according to the order of the incidence of the light from the lightsource unit LU. The concave-surface reflecting mirror 1 a as a firstreflecting mirror has a reflecting surface shaped into a concave surfacetoward the light source unit LU, while the convex-surface reflectingmirror 1 b as a second reflecting mirror has a reflecting surface shapedinto a convex surface toward the concave-surface reflecting mirror 1 a.

The divergent light emitted from a light-emitting point P1 of the lightsource unit LU comes into the concave-surface reflecting mirror 1 a viathe through hole of the convex-surface reflecting mirror 1 b. The lightreflected by the reflecting surface of the concave-surface reflectingmirror 1 a is focused or condensed at a point P2 via the through hole ofthe concave-surface reflecting mirror 1 a after being reflected by thereflecting surface of the convex-surface reflecting mirror 1 b. That is,the collector optical member 1 reflects and condenses the light from thelight source unit LU to form a primary image of the light source at theposition of the point P2. The EUV light once condensed at the point P2passes through a pinhole member (not shown) arranged in the vicinity ofthe point P2, and then becomes an approximately parallel light flux viathe collimator optical member 2 having the form of a concave-surfacereflecting mirror, so as to be shaped in a second area of apredetermined plane. The EUV light shaped in the second area enters orcomes into a fly's eye optical member 31 from the incident surface ofthe fly's eye optical member 31 provided on the predetermined plane, andis guided to an optical integrator 3 composed of a pair of fly's eyeoptical members 31 and 32. The construction and function of the fly'seye optical members 31 and 32 will be described hereinafter.

A substantial surface light source (pupil intensity distribution) havinga predetermined shape is formed in the vicinity of the light exitsurface of the optical integrator 3, i.e. at a position near thereflecting surface of the second fly's eye optical member 32 (theposition of the illumination pupil). The light from this substantialsurface light source travels via a deflecting member 4 having a planarreflecting surface, and a condenser optical system 5 having the form ofa concave-surface reflecting mirror and then exits from an illuminationoptical system IL (from 1 to 5). The position of the illumination pupilof the illumination optical system IL with the substantial surface lightsource formed as described above is the position of the entrance pupilof a below-described projection optical system PL, or the positionoptically conjugate to the entrance pupil of the projection opticalsystem PL.

The light exiting from the illumination optical system IL forms acircular-arc-shaped superposed illumination area (a first area) on thepattern surface of a mask M via a circular-arc-shaped opening (lighttransmission portion) of a field stop (not shown) arranged to beapproximately parallel and adjacent to the reflection-type mask(reticle) M. As a pattern to be transferred, for example a circuitpattern for use in a device is formed on the mask M. The illuminationoptical system IL forms a pupil intensity distribution provided by thesubstantial surface light source in the illumination pupil with thelight from the light source unit LU, and performs Kohler illumination onthe pattern on the mask M with the light from this pupil intensitydistribution.

The mask M is held by a mask stage MS movable along the Y direction suchthat the pastern surface may extend along the X-Y plane. The movement ofthe mask stage MS is measured by a laser interferometer (not shown)having a known construction. The light from the illuminated pattern ofthe mask M forms a mask pattern image on the wafer W as a photosensitivesubstrate via the reflection-type projection optical system PL. That is,as will be described hereinafter, on the wafer W, there is formed astationary exposure area (effective exposure area) having a shape of,for example, a circular arc symmetric about the Y axis.

The projection optical system PL is constructed of, as an example, afirst reflective imaging optical system forming an intermediate image ofthe pattern of the mask M, and a second reflective imaging opticalsystem forming, on the wafer W, an image of the intermediate image ofthe mask pattern (a secondary image of the pattern of the mask M). Thefirst reflective imaging optical system is constructed of fourreflecting mirrors MR1 to MR4, and the second reflective imaging opticalsystem is constructed of two reflecting mirrors MR5 and MR6. Further,the projection optical system PL is an optical system telecentric on thewafer side (image side).

The wafer W is held by a wafer stage WS two-dimensionally movable alongthe X direction and the Y direction such that the exposure surface mayextend along the X-Y plane. The movement of the wafer stage WS ismeasured by a laser interferometer (not shown) having a knownconstruction. In this manner, by carrying out a scanning exposure whilemoving the mask stage MS and the wafer stage WS along the Y direction,i.e. moving the mask M and the wafer W relative to the projectionoptical system PL along the Y direction, the pattern of the mask M istransferred to one rectangular shot area of the wafer W.

At this time, provided the projection magnification (transfermagnification) of the projection optical system PL is 1/4, for example,then the movement speed of the wafer stage WS is set to be 1/4 of themovement speed of the mask stage MS so as to carry out a synchronousscanning. Further, by repeating the scanning exposure while performing atwo-dimensional step movement of the wafer stage WS along the Xdirection and the Y direction, the pattern of the mask M is sequentiallytransferred to each shot area of the wafer W. Further, while the mask ismoved in the Y direction in the above explanation, the mask mayalternatively be moved in an oblique direction to the Y direction(oblique running).

FIG. 2 is a diagram for schematically explaining one time of thescanning exposure according the embodiment. Referring to FIG. 2, in theexposure apparatus of the embodiment, a circular-arc-shaped stationaryexposure area ER symmetric about the Y axis is formed on the surface ofthe wafer W, and the circular-arc-shaped first area symmetric about theY axis is formed on the pattern surface of the mask M, so as tocorrespond to the circular-arc-shaped effective imaging area andeffective illumination area of the projection optical system PL. Inother words, the Y direction corresponds to the normal direction of thecircular arc sides through the center of the circular arc profile (outershape) of the first area and the stationary exposure area ER, while theX direction corresponds to the perpendicular direction to the Ydirection. When transferring the pattern of the mask M to onerectangular shot area SR of the wafer W by one time of the scanningexposure, the circular-arc-shaped exposure area ER moves from ascan-starting position shown by the solid line in the figure down to ascan-ending position shown by the broken line in the figure.

In the optical integrator 3, the first fly's eye optical member 31includes a plurality of first mirror elements (first optical elements)31 a as shown in FIG. 3. The plurality of first mirror elements 31 aeach have the form of a concave-surface reflecting mirror, and arearranged in parallel arrays on a predetermined plane in the positionoptically conjugate to the pattern surface of the mask M, i.e. theirradiation surface of the illumination optical system IL. The secondfly's eye optical member 32 includes a plurality of second mirrorelements 32 a (second optical elements) as shown in FIG. 4. Theplurality of second mirror elements 32 a each have the form of aconcave-surface reflecting mirror, and are arranged in parallel arraysto correspond optically to the plurality of first mirror elements 31 ain an one-to-one manner.

In FIG. 3, in an incident surface of the first fly's eye optical member31, an x1 direction is defined as a direction corresponding to the Xdirection, and a y1 direction is defined as the perpendicular directionto the x1 direction in the incident surface. Further, the incidentsurface of the first fly's eye optical member 31 refers to an areaoccupied by the reflecting surfaces of the plurality of first mirrorelements 31 a within the predetermined plane. Likewise, in FIG. 4, in anincident surface of the second fly's eye optical member 32, an x2direction is defined as a direction corresponding to the X direction,and a y2 direction is defined as the perpendicular direction to the x2direction in the incident surface. Further, the incident surface of thesecond fly's eye optical member 32 refers to an area occupied by thereflecting surfaces of the plurality of second mirror elements 32 awithin the predetermined plane. That is, the y1 and y2 directions inFIGS. 3 and 4 correspond to the scanning direction (the Y direction) ofthe mask M and the wafer W. For the purpose of clarifying the drawings,FIGS. 3 and 4 show only some of the many mirror elements 31 a and 32 aconstituting the pair of fly's eye optical members 31 and 32.

As shown in FIG. 3, the first fly's eye optical member 31 is constructedby arranging the first mirror elements 31 a having a circular arcprofile (outer shape) in a matrix. That is, the first mirror elements 31a are arranged to align in the y1 direction such that the circular arcsides lie next to each other, and to align in the x1 direction such thatthe two circular arc ends lie next to each other. As described above,the first mirror elements 31 a each have the circular arc profile forthe purpose of forming the first area having a circular arc profile onthe mask M and, furthermore, forming the circular-arc-shaped stationaryexposure area ER on the wafer W, to correspond to thecircular-arc-shaped effective imaging area and effective illuminationarea of the projection optical system PL.

When illuminating the first area having a circular arc profile, anoptical element having a circular arc profile can be adopted as anoptical element having the profile corresponding to the first area. Forexample, the profile of at least one optical element is similar to theprofile of the first area in shape, but different from the profile ofthe first area in posture, curvature, aspect ratio between the Xdirection and the Y direction, and the like. Further, the first area andoptical element are not limited to a circular arc profile. Whenilluminating the first area having a rectangular profile, an opticalelement having a rectangular profile can be adopted as an opticalelement having the profile corresponding to the first area. At thistime, the profile of the optical element is similar to the profile ofthe first area in shape, but different from the profile of the firstarea in posture, curvature, aspect ratio between the X direction and theY direction, and the like. Further, the profile of the first area maydiffer from the profile of the optical element. For example, the opticalelement may have a rectangular profile, and be configured such that theillumination light reflected by the optical element forms the first areahaving a circular arc profile by an optical system provided between theoptical element and the first area. In addition, it is also possible toilluminate the first area in various shapes and use an optical elementhaving a profile corresponding to the various shapes of the first area.

On the other hand, as shown in FIG. 4, the second fly's eye opticalmember 32 is constructed by arranging the second mirror elements 32 ahaving, for example, a near-square rectangular profile in a matrix. Thatis, the second mirror elements 32 a are arranged to align in the x2direction and the y2 direction such that the rectangular sides lie nextto each other. The second mirror elements 32 a each have the near-squarerectangular profile for the purpose of forming a small light sourceshaped into an approximate circle at or in the vicinity of the surfaceof each second mirror element 32 a. Further, the profile of the secondmirror elements 32 a is not limited to the shape of square or rectangle,but may be a shape of polygon other than tetragon (i.e., from triangleto octagon, and the like). Further, in order to minimize the light loss,a shape allowing for tight arrangement is preferable (allowing theoptical elements to be arranged without space therebetween).

The envelope curve of the aggregate of the respective first mirrorelements 31 a of the first fly's eye optical member 31 is elliptical forthe purpose of improving the illumination efficiency because, as will bedescribed hereinafter, the cross-section shape of the incoming lightflux to the optical integrator 3 (i.e. the incident light flux on thefirst fly's eye optical member 31) is elliptical. Further, the envelopecurve of the aggregate of every second mirror element 32 a of the secondfly's eye optical member 32 is approximately circular because of theapproximately circular profile of the pupil intensity distribution (thesubstantial surface light source) formed in the illumination pupil inthe vicinity of the light exit surface of the optical integrator 3 (i.e.the light exit surface of the second fly's eye optical member 32).

Further, the envelope curve of the aggregate of the first mirrorelements 31 a is not limited to the shape of ellipse, but may take anyshape which is longer in the x1 direction than in the y1 direction. Thefirst mirror elements 31 a may be arranged to draw the envelope curve invarious shapes such as rectangle, polygon, oval, and the like. Further,the envelope curve of the aggregate of the second mirror elements 32 ais not limited to the shape of approximate circle, and the second mirrorelements 32 a may be arranged to draw the envelope curve in variousshapes such as true circle, ellipse, oval, rectangle, polygon, and thelike.

In the embodiment, the incoming light flux to the optical integrator 3is wavefront-divided by the plurality of first mirror elements 31 a inthe first fly's eye optical member 31. The light fluxes reflected by therespective first mirror elements 31 a comes into the correspondingsecond mirror elements 32 a in the second fly's eye optical member 32.The light fluxes reflected by the respective second mirror elements 32 ailluminate the circular-arc-shaped first area on the mask M in asuperposed manner via the deflecting member 4 and condenser opticalsystem 5 as a light guiding optical system.

Prior to explaining the characteristic construction and function of theembodiment, some problems in the conventional art will be describedbelow. Referring to FIG. 1, the light from the light source unit LU isguided to the mask M after being folded at the first fly's eye opticalmember 31 and the second fly's eye optical member 32. In order that theincoming light to the first fly's eye optical member 31 might not beblocked by the second fly's eye optical member 32, and the outgoinglight from the second fly's eye optical member 32 might not be blockedby the first fly's eye optical member 31, it is not possible to make thelight incident vertically by placing the first fly's eye optical member31 and second fly's eye optical member 32 face-to-face or head-on, butit is necessary to make the light incident obliquely by laterallyshifting the first fly's eye optical member 31 and second fly's eyeoptical member 32 to some extent along the sheet surface of FIG. 1.

In this case, the second mirror elements 32 a constituting the secondfly's eye optical member 32 see the first mirror elements 31 aconstituting the first fly's eye optical member 31 in an obliquedirection (a direction oblique to or inclined with respect to the normaldirection of the incident surface of the second fly's eye optical member32). To express it in another way, the first mirror elements 31 a lookdistorted as viewed from the second mirror elements 32 a. Therefore,although the plurality of second mirror elements 32 a project therespectively corresponding first mirror elements 31 a onto theirradiated pattern surface of the mask M as the irradiation surface, dueto the effect of seeing the first mirror elements 31 a from this obliquedirection, the images of the first mirror elements 31 a projected ontothe mask M cannot be correctly similar in shape to the first mirrorelements 31 a.

In other words, a distortion arises from the relative disposition andthe like between the first fly's eye optical member 31 and the secondfly's eye optical member 32. As a result, the plurality of light fluxeswavefront-divided by the plurality of first mirror elements 31 a formevery circular-arc-shaped illuminating field on the pattern surface ofthe mask M off the desired circular-arc-shaped first area, andconsequently a light loss arises from a so-called overlap error of theilluminating fields.

Next, the characteristic construction of the embodiment of the presentteaching will be explained. The optical integrator 3 is an opticalelement which uniformizes the illuminance distribution in the first areaby wavefront-dividing a light flux into a plurality of light fluxes and,superposing these plurality of light fluxes on the irradiation surface(such as the pattern surface of the mask M and, furthermore, theexposure surface of the wafer W). Therefore, the optical integrator 3can have a necessary number of optical elements (such as the mirrorelements 31 a and 32 a) for the uniformization. Further, because theuniformization is comparatively independent between the verticaldirection (such as the y1 direction and y2 direction), and thehorizontal direction (such as the x1 direction and x2 direction), it isalso possible to have a certain number or more of rows of opticalelements both in the horizontal direction and in the vertical direction.

Here, suppose that the number of rows of the first mirror elements 31 ain the first fly's eye optical member 31 is n in the x1 direction.Further, suppose that the envelope curve of the aggregate of respectivefirst mirror elements 31 a of the first fly's eye optical member 31 iscircular, and its diameter is Df. In this case, the dimension of themirror elements 31 a is Df/n in the x1 direction. As the number of rowsn in the x1 direction is greater, it is more preferable for theuniformization, and the number may be five or more.

Suppose that the interval between the first fly's eye optical member 31and the second fly's eye optical member 32 is Ff; the envelope curve ofthe aggregate of respective second mirror elements 32 a of the secondfly's eye optical member 32 is circular, and its diameter is Dp. Supposethat the focal distance of the light guiding optical system interposedbetween the second fly's eye optical member 32 and the mask M, i.e., thefocal distance of the condenser optical system 5, is Fc. Further, incase of the construction without interposing an optical system havingpower between the second fly's eye optical member 32 and the mask M, itis possible to consider that the distance from the second fly's eyeoptical member 32 to the mask M is Fc.

Provided that the dimension of the circular-arc-shaped first area to beformed on the mask M is Wi along the X direction, and provided that thenumerical aperture required for the incident light fluxes on the mask Mis NAi, then the relations shown in the following formulas (1) and (2)hold. Further, although it is necessary to add production error and thelike in the optical elements, the influence of the production error andthe like in the optical elements is ignored here for simplifying theexplanation.Wi≈(Df/n)×(Fc/Ff)  (1)NAi≈Dp/(2×Fc)  (2)

The formula (1) corresponds to the fact that each of the mirror elements31 a of the first fly's eye optical member 31 is optically conjugatewith the pattern surface of the mask M, and its imaging magnification isFc/Ff. The formula (2) corresponds to the fact that each of the mirrorelements 32 a of the second fly's eye optical member 32 performs thefunction of an aperture stop. Now, “Setting a wide interval for the sumof the diameters” is none other than setting a small value of theright-hand term I in the following formula (3).(Df+Dp)/Ff=I  (3)

Hereinbelow, observation will be made with respect to the restriction onthe value of the right-hand term I of the formula (3) by the formulas(1) and (2). The specifications of the exposure apparatus determine thedimension Wi of the circular-arc-shaped first area along the Xdirection, and the numerical aperture NAi of the incident light flux onthe mask M. From the standpoint of designing the illumination opticalsystem IL, the Wi and NAi are constants. Thus, the formulas (1) and (2)are modified as shown in the following formulas (4) and (5). Further, bysubstituting the formulas (4) and (5) into the formula (3), a relationshown in the following formula (6) is obtained.Df≈Wi×n×(Ff/Fc)  (4)Dp≈NAi×(2×Fc)  (5)I≈Wi×n/Fc+2×NAi×(Fc/Ff)  (6)

Referring to the formula (6), it is obvious how to reduce the value ofthe left-hand term I. First, it is reasonable to reduce the number ofrows n of the mirror elements 31 a of the first fly's eye optical member31 in the x1 direction. As described above, however, the number of rowsn is a variant which cannot be reduced but should rather be expected tobe increased for a sufficient uniformization of the illuminancedistribution from the standpoint of optical design. As described above,the Wi and NAi are treated as constants. The other variants left on theright-hand side of the formula (6) are only the interval Ff between thepair of fly's eye optical members 31 and 32, and the focal distance Fcof the condenser optical system 5.

In this case, the only way to reduce the value of I is to set a largefocal distance Fc of the condenser optical system 5 and, at the sametime, set a wide interval Ff according to a larger enlargement rate thanthat of the focal distance Fc. However, as is apparent by reference tothe formula (4), if a wide interval Ff is set according to a largerenlargement rate than that of the focal distance Fc, then the diameterDf of the first fly's eye optical member 31 becomes larger. Further, asis apparent by reference to the formula (5), if a large focal distanceFc is set, then the diameter Dp of the second fly's eye optical member32 becomes larger.

As a result, the size of the optical integrator 3 becomes large, andconsequently the size of the illumination optical system IL becomeslarge unavoidably. Further, in order to improve the resolving power ofEUV exposure apparatuses, it is considered recently to set an evenlarger numerical aperture NAi of the incident light flux on the mask M.As is apparent by reference to the formula (6), if the numericalaperture NAi becomes even larger, then the value of the left-hand term Ialso becomes larger, thereby causing the size of the optical integrator3 to become further larger.

In the embodiment, as shown in FIG. 3, the envelope curve of theaggregate of every first mirror element 31 a of the first fly's eyeoptical member 31 is set to be an ellipse with the major axis Dfx in thex1 direction and the minor axis Dfy in the y1 direction. In this case,the above formulas (1), (3) and (4) can be rewritten as shown in thefollowing formulas (1A), (3A) and (4A).Wi≈(Dfx/n)×(Fc/Ff)  (1A)(Dfy+Dp)/Ff=I  (3A)Dfx≈Wi×n×(Ff/Fc)  (4A)

Accordingly, provided the major axis Dfx is m times the minor axis Dfy(m>1), the relationship between Dfx and Dfy is expressed as Dfx=m×Dfy,then the above formula (6) can be rewritten as shown in the followingformula (6A). Comparing the formula (6) with the formula (6A), the valueof the first right-hand term of the formula (6A) is 1/m (1/m<1) timesthe value of the first right-hand term of the formula (6). Thus, it isunderstood that the value of I becomes smaller by the difference betweenthese terms.I≈(Wi×n/Fc)/m+2×NAi×(Fc/Ff)  (6A)

Conventionally, the envelope curve of the aggregate of the respectivefirst mirror elements 31 a of the first fly's eye optical member 31 isapproximately circular because the divergent light supplied from thelight source has a constant spread angle independent of direction and acircular cross section and, furthermore, the incident light flux on thefirst fly's eye optical member 31 also has a circular cross section. Inthe embodiment, by setting the envelope curve of the aggregate of therespective first mirror elements 31 a of the first fly's eye opticalmember 31 to be elongated in the x1 direction, it is possible to reducethe value of the left-hand term I of the formula (6A) without causingthe fly's eye optical members 31 and 32 to grow in size. At this time,the envelope curve of the aggregate of the first mirror elements 31 amay have an elliptical shape elongated in the x1 direction.

Further, if the light flux having a cross-sectional shape elongated inthe x1 direction comes into the first fly's eye optical member 31, thenit is possible to maintain a high illumination efficiency at the firstfly's eye optical member 31. At this time, the collector optical member1 may be constructed to convert the light flux being emitted from thelight-emitting point P1 of the light source unit LU and having acircular cross section, i.e., the light flux having a constant spreadangle independent of direction, into a light flux having a cross sectionelongated in the x1 direction, and then cause the converted light fluxto come into the first fly's eye optical member 31. At this time, thecross section of the incident light flux on the first fly's eye opticalmember 31 from the collector optical member 1 can have an ellipticalshape elongated in the x1 direction.

In this manner, in the illumination optical system IL of the embodiment,it is possible to restrain distortion from occurring without causing theoptical integrator 3 to grow in size and, furthermore, to illuminate themask M under a required illumination condition capable of achieving ahigh light efficiency while keeping the occurrence of light loss due tothe overlap error of illuminating fields at a low level. As a result, inthe exposure apparatus of the embodiment, it is possible to carry out afavorable exposure under a favorable illumination condition by using theillumination optical system IL illuminating the mask M under a requiredillumination condition capable of achieving a high light efficiencywhile keeping the light loss small.

That is, in the embodiment, it is possible to restrain distortion fromoccurring without causing the optical integrator 3 to grow in size and,furthermore, to keep the occurrence of light loss due to the overlaperror of illuminating fields at a low level. As a result, in theexposure apparatus of the embodiment, it is possible to carry out afavorable exposure under a favorable illumination condition by using theillumination optical system IL provided with the optical integrator 3keeping the light loss small to illuminate the mask M under a requiredillumination condition capable of achieving a high light efficiency.

FIGS. 5 and 6 are diagrams schematically showing a construction of acollector optical member according to the embodiment. In FIGS. 5 and 6,an x3 direction and a y3 direction are defined as directionscorresponding to the x1 direction and the y1 direction respectively inthe incident surface of the first fly's eye optical member 31 (a secondarea), and a z3 direction is defined as a direction perpendicular toboth the x3 direction and the y3 direction. That is, in FIGS. 5 and 6,the y3 direction corresponds to the Y direction which is the scanningdirection while the x3 direction corresponds to the X directionperpendicular to the scanning direction. FIG. 5 shows the light raysalong the x3-z3 plane while FIG. 6 shows the light rays along the y3-z3plane.

The following table (1) shows the value of each element of the collectoroptical member according to the embodiment. Descriptions in the table(1) are made in accordance with the format of “Code V” which is anoptical design software product by ORA (Optical Research Associates). Inthe table (1), RDY indicates the curvature radius of a surface (or theapical curvature radius of an aspheric surface; unit: mm); THI indicatesthe distance from a present surface to the next surface i.e. a surfaceinterval (unit: mm); and RMD indicates whether a present surface is areflecting surface or a refracting surface. REFL means reflectingsurface. INFINITY means infinitely great, and if RDY is INFINITY then itmeans that the relevant surface is a flat surface.

OBJ indicates the light-emitting point P1; STO indicates the surface ofa virtual aperture stop; and IMG indicates the light condensing pointP2. Surface No. 1 indicates a virtual surface; Surface No. 2 indicatesthe reflecting surface of the concave-surface reflecting mirror 1 a asthe first reflecting mirror; and Surface No. 4 indicates the reflectingsurface of the convex-surface reflecting mirror 1 b as the secondreflecting mirror. SPS ZRN means that the reflecting surfaces of therespective reflecting mirrors 1 a and 1 b are aspheric surfaces denotedby power series. The notations of the table (1) is the same as in theaftermentioned table (2), except for the expression of aspheric surface.

TABLE (1) RDY THI RMD GLA OBJ: INFINITY 0.000000 1: INFINITY 1500.0001242: −432.83272 −949.999641 REFL SPS ZRN: SCO K: −9.4341E−01 ZP4:−1.8270E−05 ZP5: 4.3276E−04 ZP11: 4.3260E−13 ZP12: −1.9463E−12 ZP13:1.0935E−11 ZP22: −2.6779E−20 ZP23: −6.7188E−20 ZP24: −7.5913E−20 ZP25:4.5844E−19 ZP38: −2.9880E−29 ZP39: −3.1230E−27 ZP40: 2.1408E−26 ZP41:2.6357E−27 ZP56: 1.1351E−33 ZP57: −1.6723E−33 ZP58: −3.4764E−34 ZP59:7.2244E−34 ZP60: −4.0069E−33 ZP61: 3.9159E−33 STO: INFINITY −500.0000004: −0.00000 1800.000000 REFL SPS ZRN: SCO K: −1.4290E+33 ZP4:−2.5757E−04 ZP5: −1.9264E−04 ZP11: −3.4980E−11 ZP12: 3.1541E−12 ZP13:4.8114E−11 ZP22: −8.3924E−17 ZP23: 6.3352E−17 ZP24: 3.2097E−17 ZP25:−5.6027E−17 ZP38: 7.4668E−23 ZP39: −5.3416E−24 ZP40: 1.9365E−23 ZP41:5.7693E−23 ZP56: 2.3481E−28 ZP57: 3.9143E−29 ZP58: 1.4709E−30 ZP59:2.1537E−29 ZP60: 8.3116E−30 ZP61: −1.0180E−29 IMG: INFINITY 0.000000

In the embodiment, the divergent light emitted from the light-emittingpoint P1 has a constant spread angle independent of direction and acircular cross section. This divergent light having a circular crosssection is converted into a light flux having an elliptical crosssection with the major axis in the x3 direction and the minor axis inthe y3 direction via the aspheric reflecting surface of theconcave-surface reflecting mirror 1 a and the aspheric reflectingsurface of the convex-surface reflecting mirror 1 b, and is condensed atthe point P2. As a result, the light flux coming into the first fly'seye optical member 31 via the light condensing point P2 has anelliptical cross section with the major axis in the x1 direction and theminor axis in the y1 direction. In the embodiment, the ratio between themajor axis and the minor axis of the cross section of the incident lightflux on the first fly's eye optical member 31 is 2 to 1.

Further, in the above embodiment, the light source unit LU of DPP typeis used. However, without being limited to this, it is also possible touse a light source unit LU′ of LPP (Laser Produced Plasma) type in afirst modification such as that shown in FIG. 7. In the light sourceunit LU′ of LPP type, laser light is condensed on a target, and plasmais produced by the target to obtain EUV light.

The first modification shown in FIG. 7 has a similar construction tothat of the embodiment shown in FIG. 1. However, the first modificationshown in FIG. 7 uses the light source unit LU′ Of LPP type instead ofthe light source unit LU of DPP type and uses a collector optical member11 constructed to adapt to the light source unit LU′ of LPP type. Thisaspect differs from that of the embodiment shown in FIG. 1. Hereinbelow,focused on the difference with respect to the embodiment shown in FIG.1, the construction and function of the first modification shown in FIG.7 will be explained.

The light source apparatus according to the embodiment includes thelight source unit LU′ and the collector optical member 11. The lightsource unit LU′ includes a laser light source 21, a condensing lens 22,a nozzle 23, and a duct 24. In the light source unit LU′, ahigh-pressure gas composed of such as xenon (Xe) is supplied from thenozzle 23, and the gas jetted from the nozzle 23 forms a gas target 25.Then, the light (non-EUV light) emitted from the laser light source 21is condensed on the gas target 25 via the condensing lens 22.

The gas target 25 obtains energy from the condensed laser light toproduce plasma, and emits EUV light. That is, the position of the gastarget 25 is the light-emitting point P1. The EUV light emitted from thelight-emitting point P1 of the light source unit LU′ is condensed by thecollector optical member 11 having a similar form to an ellipticalconcave-surface reflecting mirror, and is then guided to the first fly'seye optical member 31 via the collimator optical member 2. The gashaving finished light emission is sucked and guided to the outsidethrough the duct 24.

FIGS. 8 and 9 are diagrams schematically showing a construction of thecollector optical member according to the first modification shown inFIG. 7. In FIGS. 8 and 9, an x4 direction and a y4 direction are definedas directions corresponding to the x1 direction and the y1 directionrespectively in the incident surface (light-receiving surface) of thefirst fly's eye optical member 31, and a z4 direction is defined as adirection perpendicular to both the x4 direction and the y4 direction.That is, in FIGS. 8 and 9, the y4 direction corresponds to the Ydirection which is the scanning direction while the x3 directioncorresponds to the X direction perpendicular to the scanning direction.FIG. 8 shows the light rays along the x4-z4 plane while FIG. 9 shows thelight rays along the y4-z4 plane. The following table (2) shows thevalue of each element of the collector optical member according to thefirst modification. In the table (2), the section of “Data in the x4direction” shows the data concerning the light rays along the x4-z4plane in FIG. 8, while the section of “Data in the y4 direction” showsthe data concerning the light rays along the y4-z4 plane in FIG. 9. OBJindicates the light-emitting point P1; Surface No. 1 indicates a virtualsurface; STO indicates the reflecting surface of the concave-surfacereflecting mirror constituting the collector optical member 11; and IMGindicates light condensing points P2 x and P2 y. ASP means an asphericsurface expressed as power series.

TABLE (2) <Data in the x4 direction> RDY THI RMD GLA OBJ: INFINITY0.000000 1: INFINITY 150.000000 STO: −256.06602 −874.264069 REFL ASP: K:−0.500000 IC: YES CUF: 0.000000 A: 0.000000E+00 B: 0.000000E+00 C:0.000000E+00 D: 0.000000E+00 IMG: INFINITY 0.000000 <Data in the y4direction> RDY THI RMD GLA OBJ: INFINITY 0.000000 1: INFINITY 150.000000STO: −266.18950 −1180.947502 REFL ASP: K: −0.600000 IC: YES CUF:0.000000 A: 0.000000E+00 B: 0.000000E+00 C: 0.000000E+00 D: 0.000000E+00IMG: INFINITY 0.000000

In the first modification shown in FIG. 7, as shown in FIG. 8, theintersection between the reflecting surface of the concave-surfacereflecting mirror constituting the collector optical member 11 and aplane parallel to the x4-z4 plane through the light-emitting point P1corresponds to part of an ellipse having one focal point at thelight-emitting point P1 and having the other focal point at the point P2x. Further, as shown in FIG. 9, the intersection between the reflectingsurface of the collector optical member 11 and a plane parallel to they4-z4 plane through the light-emitting point P1 corresponds to part ofanother ellipse having one focal point at the light-emitting point P1and having the other focal point at the point P2 y.

In the first modification, the divergent light supplied from thelight-emitting point P1 also has a constant spread angle independent ofdirection and a circular cross section. In this divergent light having acircular cross section, the light rays along the x4-z4 plane arecondensed at the point P2 x, via the aspheric reflecting surface of thecollector optical member 11, while the light rays along the y4-z4 planeare condensed at the point P2 y, away from the collector optical member11 farther than the P2 x via the aspheric reflecting surface of thecollector optical member 11. In this manner, the divergent light havinga circular cross section from the light-emitting point P1 is converted,via the aspheric reflecting surface of the collector optical member 11,into a light flux having an elliptical cross section with the major axisin the x4 direction and the minor axis in the y4 direction.

As a result, the incident light flux on the first fly's eye opticalmember 31 has an elliptical cross section with the major axis in the x1direction and the minor axis in the y1 direction. In the firstmodification, the ratio between the major axis and the minor axis of thecross section of the incident light flux on the first fly's eye opticalmember 31 is 1.1 to 1. The collector optical member 11 reflects thelight from the light source unit LU′, and condenses the same to form aprimary image of the light source. In the first modification, thecondensing point P2 x of the light rays along the x4-z4 plane does notcoincide with the condensing point P2 y of the light rays along they4-z4 plane. Therefore, it is difficult to sufficiently narrow the lightflux on the mirror elements 32 a of the second fly's eye optical member32. However, there are no particular problems if the light source issmall enough in size and the light flux does not spread out (go out) thecontour of the mirror elements 32 a.

In the collector optical member 11 according to the first modification,in the incident light flux on the first fly's eye optical member 31 ofthe optical integrator 3, for example, the light rays propagating withinthe y4-z4 plane are condensed at the condensing position P2 y betweenthe mask M and the light-emitting point P1 of the light source unit LU′(i.e. the light source), while the light rays propagating within thex4-z4 plane are condensed at the condensing position P2 x between thecondensing position P2 y and the light-emitting point P1 of the lightsource unit LU′.

To express it in another way, in the light from the light source unitLU′, the light rays to be condensed at the condensing position P2 ybetween the mask M and the light-emitting point P1 of the light sourceunit LU′ propagate through the y4-z4 cross section of the condensingsurface of the concave-surface reflecting mirror constituting thecollector optical member 11. At the same time, the light rays to becondensed at the condensing position P2 x between the condensingposition P2 y and the light-emitting point P1 of the light source unitLU′ propagate through the x4-z4 cross section of the condensing surface.In the collector optical member 11, the curvature of the condensingsurface differs between the y4-z4 cross section including the y4direction, and the x4-z4 cross section including the x4 direction (thecross section perpendicular to the y4-z4 cross section). For example,the curvature radius of the x4-z4 cross section is larger than that ofthe y4-z4 cross section with respect to the condensing surface.

That is, in the first modification shown in FIG. 7, the X direction isthe direction in which the light condensed by the condensing surface ofthe x4-z4 cross section of the collector optical member 11 is projectedin the superposed illumination area by the optical systems (2 to 5)between the collector optical member 11 and the superposed illuminationarea on the mask M (the first area). Further, the Y direction is thedirection in which the light condensed by the condensing surface of they4-z4 cross section of the collector optical member 11 is projected inthe superposed illumination area by the optical systems (2 to 5).

Further, in the above explanations, the plurality of first mirrorelements 31 a of the first fly's eye optical member 31 correspondoptically to the plurality of second mirror elements 32 a of the secondfly's eye optical member 32. Here, The term “correspond optically” meansthat, as shown in FIG. 10 for example, the light reflected by one of theplurality of first mirror elements 31 a is reflected by any one of theplurality of second mirror elements 32 a. In particular, in FIG. 10, thelight rays reflected by the first mirror elements 31 a 1, 31 a 2, 31 a3, 31 a 4 and 31 a 5 comes into the second mirror elements 32 a 1, 32 a2, 32 a 3, 32 a 4 and 32 a 5, respectively.

That is, the first mirror element 31 a 1 corresponds optically to thesecond mirror element 32 a 1. Likewise, the first mirror elements 31 a 2to 31 a 5 correspond optically to the second mirror elements 32 a 2 to32 a 5, respectively. However, the plurality of first mirror elements 31a do not need to correspond to the plurality of second mirror elements32 a in a one-to-one manner, but the light reflected by one first mirrorelement and the light reflected by another first mirror element may bereflected by one identical second mirror element. Alternatively, theremay be some second mirror elements which do not reflect the lightreflected by the first mirror elements. When changing the illuminationcondition, it is possible to change the optically corresponding relationbetween the plurality of first mirror elements and the plurality ofsecond mirror elements.

Further, even with an elliptical intensity distribution in the crosssection of the incident light flux on the first fly's eye optical member31, it is still possible to form a circular intensity distribution inthe cross section (pupil plane) of the incident light flux on the secondfly's eye optical member 32. Further, the intensity distribution in thepupil plane is not limited to a circular shape, but may be bipolar,quadrupolar, ring-like, square, elliptical, and the like. In such cases,it is still possible to equalize the resolving power of the patternformed on the wafer W in two orthogonal directions (for example, the Xdirection and the Y direction). At this time, it is possible to adjustthe optically corresponding relation between the plurality of firstmirror elements and the plurality of second mirror elements.

Nevertheless, in the first modification shown in FIG. 7, the curvatureradius of the condensing surface of the collector optical member 11differs between the y4-z4 cross section including the y4 direction andthe x4-z4 cross section including the x4 direction. Thus the condensingpoint P2 x of the light along the x4-z4 plane does not coincide with thecondensing point P2 y of the light along the y4-z4 plane in the opticalaxis direction. As a result, a defocused light source image 41 (asecondary image of the light source) is formed, as shown in FIG. 11, inthe reflecting surface of one second mirror element 32 a of the secondfly's eye optical member 32.

Because astigmatism arises from the influence of the cross-sectionalshape of the light flux wavefront-divided by the first fly's eye opticalmember 31 (i.e. an anisotropic influence of the curvature of thecondensing surface of the collector optical member 11), the profile ofthe light source image 41 becomes longer in one direction than inanother. There are no particular problems if the light source image 41(i.e. the incident light flux on the second mirror element 32 a) doesnot spread out the contour of the reflecting surface of the secondmirror element 32 a. However, if the light source image 41 is too largeand consequently spreads out the contour of the reflecting surface ofthe second mirror element 32 a, then it not only gives rise to lightloss but also unavoidably causes the overlap error of illuminatingfields to occur in the superposed illumination area on the mask M.

Generally, in order to uniformize the illuminance distribution in thesuperposed illumination area on the mask M, there is a tendency toincrease the number of wavefront divisions at the first fly's eyeoptical member 31, that is, a tendency to reduce the size of thereflecting surfaces of the first mirror element 31 a and the secondmirror element 32 a. Reducing the size of the second mirror element 32 abrings about a higher possibility that the light source image 41 spreadsout the contour of the reflecting surface of the second mirror element32 a to give rise to light loss and collapse of the superposedillumination area.

In a second modification, the reflecting surface of one first mirrorelement 31 a is shaped into a toroidal surface to keep a small size of alight source image 42 formed on one second mirror element 32 a asschematically shown in FIG. 12, and furthermore, to avoid the occurrenceof light loss and collapse of the superposed illumination area. Inparticular, in the second modification, the reflecting surface of thefirst mirror element 31 a is formed into a toroidal surface withdifferent surface curvatures from each other along the x1 direction andalong the y1 direction.

In other words, a required curvature along the x1 direction and arequired curvature along the y1 direction are given to the reflectingsurface of the first mirror element 31 a such that the light sourceimage 41, which is elongated in one direction and obtained as thereflecting surface of the first mirror element 31 a is spherical, maybecome the light source image 42 which is comparatively small in sizeand not much defocused as a whole. As a result, the reflecting surfaceof the first mirror element 31 a has different curvatures from eachother along the x1 direction and along the y1 direction.

However, if the size of the light source image 42 is too small, then themultilayer film forming the reflecting surface of the second mirrorelement 32 a may become liable to thermal deformation and/or damage dueto light illumination. In such cases, by appropriately adjusting thecurvatures of the reflecting surface of the first mirror element 31 aalong the x1 direction and along the y1 direction, as shown in FIG. 13,it is possible to actively form a light source image 43 comparativelylarge in size and substantially defocused as a whole, therebydiminishing thermal deformation and damage of the multilayer film.

As a particular numerical example, with respect to the condensingsurface of the concave-surface reflecting mirror constituting thecollector optical member 11, the ratio between the curvature Cy4 alongthe y4 direction and the curvature Cx4 along the x4 direction may be,for example, 5 to 6 or 7 to 8. In such cases, it is possible to set theratio between the curvature Cx1 along the x1 direction and the curvatureCy1 along the y1 direction to be, for example, 5 to 6, 6 to 5, 7 to 8,or 8 to 7, for the reflecting surface of the first mirror element 31 a.Then, when the ratio between the curvature Cy4 and the curvature Cx4 is5 to 6 with the collector optical member 11, provided the ratio betweenthe curvature Cx1 and the curvature Cy1 is set to be 5 to 6 for thefirst mirror element 31 a, then it is possible to obtain the lightsource image 42 comparatively small in size in the second mirror element32 a and, furthermore, to avoid the occurrence of light loss andcollapse of the superposed illumination area.

Further, when the ratio between the curvature Cy4 and the curvature Cx4is 5 to 6 with the collector optical member 11, provided the ratiobetween the curvature Cx1 and the curvature Cy1 is set to be 7 to 8 forthe first mirror element 31 a, then it is possible to obtain the lightsource image 43 comparatively large in size in the second mirror element32 a and, furthermore, to diminish thermal deformation and damage of themultilayer film. At this time, if it is possible to correct (compensate)for the influence on the illumination efficiency on the mask M due tothe varying curvatures with direction in the condensing surface of thecollector optical member 11 and in the reflecting surface of the firstmirror element 31 a by adjusting the relation between the curvature ofthe collector optical member 11 and the curvature of the first mirrorelement 31 a, then the reflecting surface of the second mirror element32 a may be spherical as it is. If it is not possible to perform thecorrection by adjusting the curvature relation between the collectoroptical member 11 and the first mirror element 31 a, then it is possibleto perform the correction by forming the reflecting surface of thesecond mirror element 32 a into the shape of a required toroidalsurface.

In the second modification, it is not necessary to form a toroidalreflecting surface for every first mirror element 31 a. By forming atoroidal reflecting surface each for a necessary number (at least one)of the reflecting surface of the first mirror elements 31 a, it is stillpossible to obtain the effect of avoiding the occurrence of light lossand collapse of the superposed illumination area, or the effect ofdiminishing thermal deformation and damage of the multilayer film. Theseeffects are obtainable by satisfying the following formula (7), forexample, in terms of the curvature Cx1 along the x1 direction and thecurvature Cy1 along the y1 direction with respect to the reflectingsurface of one first mirror element 31 a.1.0<Cx1/Cy1<1.2, or 1.0<Cy1/Cx1<1.2  (7)

In the above explanations, a technique of forming a toroidal reflectingsurface for the reflecting surface of the first mirror element 31 a isapplied to the construction of the first modification shown in FIG. 7.However, without being limited to the construction of the firstmodification shown in FIG. 7, it is also possible to apply the techniqueof forming a toroidal reflecting surface for the reflecting surface ofthe first mirror element 31 a to the construction of the embodimentshown in FIG. 1. In the construction of the embodiment shown in FIG. 1,the condensing points P2 of the light from the collector optical member1 coincide with each other independently of direction.

As a result, as shown in the left-hand figure of FIG. 14, the lightsource image 42 comparatively small in size is formed on the reflectingsurface of one second mirror element 32 a, and the multilayer film maybe liable to thermal deformation and/or damage due to lightillumination. In such cases, in the construction of the embodiment shownin FIG. 1, by appropriately adjusting the curvature Cx1 along the x1direction and the curvature Cy1 along the y1 direction with thereflecting surface of the first mirror element 31 a, as shown in theright-hand figure of FIG. 14, it is also possible to actively form thelight source image 43 comparatively large in size and substantiallydefocused as a whole, thereby diminishing thermal deformation and damageof the multilayer film.

In the above manner, in the illumination optical system IL according theabove embodiment and modifications, the first area longer in the Xdirection than in the Y direction, typically the circular-arc-shapedsuperposed illumination area elongated in the X direction, is formed onthe pattern surface of the mask M. The optical apparatus of a firstaspect includes the collector optical member 1(11) which is arranged inan optical path between the light source unit LU (LU′) and the mask M,and condenses the light from the light source unit LU (LU′) to form, ona predetermined plane, the second area (the incident light flux area ofan elliptical shape with the major axis in the x1 direction and theminor axis in the y1 direction) longer in the x1 direction(corresponding to the X direction) than in the y1 direction(corresponding to the Y direction); and the first fly's eye opticalmember 31 having the plurality of first mirror elements 31 a which areprovided within the predetermined plane including the second area toguide the light from the collector optical member 1 (11) to the firstarea.

The optical apparatus of a second aspect includes the first fly's eyeoptical member 31 which is provided in an optical path between the lightsource unit LU (LU′) and the mask M, and aligns, in a predeterminedplane, the plurality of first mirror elements 31 a having a profilelonger in the x1 direction (corresponding to the X direction) than inthe y1 direction (corresponding to the Y direction) while an aggregateof the aligned first mirror elements 31 a has different lengths fromeach other in the y1 direction and in the x1 direction; and the secondfly's eye optical member 32 which is provided in an optical path betweenthe first fly's eye optical member 31 and the mask M, and has theplurality of second mirror elements 32 a arranged to correspondoptically to the first mirror elements 31 a.

The optical apparatus of a third aspect includes the first fly's eyeoptical member 31 which is provided within a predetermined planeincluding the second area (the incident light flux area of an ellipticalshape with the major axis in the x1 direction and the minor axis in they1 direction), and has the plurality of first mirror elements 31 a. Atleast one mirror element of the plurality of first mirror elements 31 ahas an optical surface (i.e. a reflecting surface) with differentsurface curvatures from each other along the y1 direction (a thirddirection) and along the x1 direction (a fourth direction) within thesurface perpendicular to the second area. Generally, if the firstoptical elements constituting the first fly's eye optical member arereflecting members, then the optical surface with different curvaturesfrom each other in two directions is a reflecting surface, a diffractingsurface, or the like. On the other hand, if the first optical elementsare light-transmissive members, then the optical surface with differentcurvatures from each other in two directions is a lens surface, adiffracting surface, or the like.

In the illumination optical system IL according the above embodiment andmodifications, it is possible to restrain distortion from occurringwithout causing the optical integrator 3 to grow in size and,furthermore, to illuminate the mask M under a required illuminationcondition capable of achieving a high light efficiency while keeping theoccurrence of light loss due to the overlap error of illuminating fieldsat a low level. As a result, in the exposure apparatus according to theabove embodiment and modifications, it is possible to carry out afavorable exposure under a favorable illumination condition by using theillumination optical system IL illuminating the mask M under a requiredillumination condition capable of achieving a high light efficiencywhile keeping the light loss small.

In the first aspect and the second aspect, it may be configured that thesecond area (the incident light flux area of an elliptical shape withthe major axis in the x1 direction and the minor axis in the y1direction; the area of the incident light flux on the first fly's eyeoptical member 31) is longer in the x1 direction than in the y1direction by 1.1 times or more. Further, provided the aspect ratio ofthe second area is 1 to α in length between the y1 direction and the x1direction, then it may be configured to satisfy the condition of α=1.1or more. Further, it is possible to let a not exceed 4.0.

In the first aspect and the second aspect, with the configuration ofaligning the mirror elements 31 a of the optical integrator 3 onlywithin the second area, it is possible to further diminish light loss.Further, it is also possible to configure the aggregate of the mirrorelements 31 a to be longer in the x1 direction than in the y1 directionby 1.1 times or more. Further, provided the aspect ratio of theaggregate of the mirror elements 31 a is 1 to α in length between the y3direction and the x1 direction, then it may be configured to satisfy thecondition of α=1.1 or more. Further, it is possible to let a not exceed4.0.

In the first aspect and the second aspect, it is possible to configurethe cross section of the incoming light flux to the optical integrator 3(furthermore, the incident light flux on the first fly's eye opticalmember 31) to be longer in the x1 direction than in the y1 direction by1.1 times or more. Further, provided the aspect ratio of the crosssection of the incoming light flux to the optical integrator 3 is 1 to αin length between the y1 direction and the x1 direction, then it may beconfigured to satisfy the condition of α=1.1 or more. Further, it ispossible to let a not exceed 4.0.

Further, in the above embodiment and modifications, the illuminationarea elongated in the X direction intersecting the Y direction, i.e.,the circular-arc-shaped illumination area elongated in the X direction,is formed on the pattern surface of the mask M. The first fly's eyeoptical member 31 of the optical integrator 3 is constructed by aligningthe plurality of mirror elements 31 a having a profile corresponding tothe illumination area, i.e., a circular arc profile elongated in the x1direction (corresponding to the X direction), in the y1 direction(corresponding the Y direction) and in the x1 direction. In the firstfly's eye optical member 31, the aggregate of the aligned mirrorelements 31 a has different lengths from each other in the y1 directionand in the x1 direction.

To express it in another way, the light-receiving surface (incidentsurface) of the first fly's eye optical member 31 has different lengthsfrom each other in the y1 direction and in the x1 direction. To expressit in still another way, the light-receiving surface of the first fly'seye optical member 31 has different numbers of the elements aligned inthe y1 direction and in the x1 direction. By this configuration, in theabove embodiment and modifications, it is possible to restraindistortion from occurring without causing the optical integrator 3 togrow in size and, furthermore, to keep the occurrence of light loss dueto the overlap error of illuminating fields at a low level. As a result,in the exposure apparatus according to the above embodiment andmodifications, it is possible to carry out a favorable exposure under afavorable illumination condition by using the illumination opticalsystem IL provided with the optical integrator 3 keeping the light losssmall to illuminate the mask M under a required illumination conditioncapable of achieving a high light efficiency.

Provided the aspect ratio of the aggregate of the aligned mirrorelements 31 a is 1 to α between the y1 direction and the x1 direction,then it may be configured to satisfy the condition of α=1.1 or more.Further, it is also possible to configure the aggregate of the alignedmirror elements 31 a to be longer in the x1 direction than in the y1direction by 1.1 times or more. Further, it is also possible toconfigure the aggregate of the mirror elements 31 a with 20 rows or morealigned in the y1 direction and 5 rows or more aligned in the x1direction.

Further, while the collimator optical member 2 is provided between thecollector optical member 1 and the optical integrator 3 in the aboveexplanations, it is not limited to this configuration. That is, theoptical apparatus may also be configured to cause the light from thelight source unit LU (LU′) to come into the first fly's eye opticalmember 31 of the optical integrator 3 without passing an optical memberhaving power (an optical member such as the collimator optical member2). Here, the power of an optical member is the reciprocal of the focaldistance of that optical member.

Further, the present teaching is explained above based on an exposureapparatus of near pupil type. Here, the exposure apparatus of near pupiltype refers to an exposure apparatus including a projection opticalsystem in which the entrance pupil is positioned on the projectionoptical system side with respect to the object surface (corresponding tothe pattern surface of the mask M). However, without being limited tothe exposure apparatus of near pupil type, it is also possible to applythe present teaching in the same manner to an exposure apparatus of farpupil type. The exposure apparatus of far pupil type refers to anexposure apparatus including a projection optical system in which theentrance pupil is positioned on the opposite side to the projectionoptical system across the object surface.

In particular, in the exposure apparatus of far pupil type, the lightfrom the light source unit LU (LU′) passes the collector optical member1 (the collector optical member 11), and then comes into the opticalintegrator 3 in the illumination optical system IL via the collimatoroptical member 2. Thereafter, the light via the optical integrator 3forms the circular-arc-shaped first area on the mask M via an obliqueincident mirror (a flat-surface reflecting mirror). That is, the lightvia the second fly's eye optical member 32 of the optical integrator 3is guided to the pattern surface of the mask M as the irradiationsurface not via any optical member having power (an optical member suchas the condenser optical system 5). Further, it is also possible tointerpose an optical member having power in the optical path between theoptical integrator 3 and the irradiation surface. Further, it may alsobe configured not to interpose an optical member having power such asthe collimator optical member 2 between the collector optical member 1(11) and the optical integrator 3.

Further, in the above explanations, the first mirror elements 31 a inthe first fly's eye optical member 31 each have a circular arc profile,while the second mirror elements 32 a in the second fly's eye opticalmember 32 each have a rectangular profile. However, without beinglimited to these profiles, various forms are adaptable for the profileof each optical element, as well as for the positive or negative powerof each optical element. Further, it is also possible to use refractingoptical elements or diffracting optical elements instead of the mirrorelements.

In the above explanations, the ratio between the major axis and theminor axis of the cross section of the incident light flux on the firstfly's eye optical member 31 is 2 to 1 or 1.1 to 1. However, the ratiobetween the major axis and the minor axis of the cross section of theincident light flux on the first fly's eye optical member 31 is notlimited to this but can be a to 1 (where α=1.1 or more). Further, it ispossible to make a to be not more than 4.0.

In the illumination method according to a sixth aspect, in the patternsurface of the mask M, the light from the light source unit LU (LU′)forms the first area longer in the X direction than in the Y direction,i.e., the circular-arc-shaped superposed illumination area elongated inthe X direction. This illumination method includes: condensing the lightfrom the light source and guiding the same to the second area in apredetermined plane, wavefront-dividing the light into a plurality oflight fluxes each having a profile longer in a fourth directionintersecting a third direction than in the third direction in thepredetermined plane, and guiding the plurality of wavefront-dividedlight fluxes to the first area. The second area has a shape longer inthe fourth direction than in the third direction (the incident lightflux area long in the x1 direction but short in the y1 direction), andthe plurality of light fluxes in the predetermined plane are alignedalong the third direction and the fourth direction.

The optical apparatus producing method according to a ninth aspect isconfigured to produce an optical apparatus used for uniformlyilluminating an illumination area longer in the X direction than in theY direction with the light from the light source unit LU (LU′). Theoptical apparatus producing method includes obtaining a collectoroptical member forming, in a predetermined plane, the second area longerin a fourth direction intersecting a third direction than in the thirddirection (the incident light flux area long in the x1 direction butshort in the y1 direction) by condensing the light from the lightsource, and setting the first fly's eye optical member having aplurality of first optical elements within the predetermined planeincluding the second area.

The optical apparatus producing method according to a tenth aspect isconfigured to produce an optical apparatus used for uniformlyilluminating an illumination area longer in the X direction than in theY direction with the light from the light source unit LU (LU′). Theoptical apparatus producing method includes preparing a plurality offirst optical elements each having a profile longer in a fourthdirection intersecting a third direction than in the third direction,and obtaining a first fly's eye optical member including such anaggregate of the plurality of first optical elements aligned in thethird direction and the fourth direction as has different lengths fromeach other in the third direction and in the fourth direction.

In the above embodiment, instead of the mask M, a variable patternformation apparatus can be used to form a predetermined pattern based ona predetermined electric data. Further, as the variable patternformation apparatus, it is possible to use, for example, a spatial lightmodulation element including a plurality of reflecting elements to bedriven based on the predetermined electric data. An exposure apparatususing such a spatial light modulation element is disclosed in, forexample, U.S. Patent Application Publication No. 2007/0296936. Further,other than the reflective spatial light modulator of non-light-emittingtype as mentioned above, it is also possible to use a transmissivespatial light modulator or an image display element ofself-light-emitting type.

The exposure apparatus of the embodiment described above is produced byassembling the various subsystems including the respective constitutiveelements as defined in claims so that the predetermined mechanicalaccuracy, electric accuracy and optical accuracy are maintained. Inorder to secure the various accuracies, those performed before and afterthe assembling include the adjustment for achieving the optical accuracyfor the various optical systems, the adjustment for achieving themechanical accuracy for the various mechanical systems, and theadjustment for achieving the electric accuracy for the various electricsystems. The steps of assembling the various subsystems into theexposure apparatus include, for example, the mutual mechanicalconnection, wiring connection of the electric circuits, and pipingconnection of the air pressure circuits among the various subsystems. Itgoes without saying that the steps of assembling the respectiveindividual subsystems are performed before performing the steps ofassembling the various subsystems into the exposure apparatus. When thesteps of assembling the various subsystems into the exposure apparatusare completed, the overall adjustment is performed to secure the variousaccuracies as the entire exposure apparatus. It is preferable that theexposure apparatus is produced in a clean room in which the temperature,the cleanness, etc. are managed.

Next, an explanation will be made about a device production method usingthe exposure apparatus or exposure method according to the aboveembodiment. FIG. 15 is a flowchart showing steps of producing asemiconductor device. As shown in FIG. 15, in the steps of producing thesemiconductor device, a metal film is vapor-deposited on a wafer W whichis to serve as a substrate of the semiconductor device (Step S40); and aphotoresist as a photosensitive material is coated on thevapor-deposited metal film (Step S42). Subsequently, a pattern formed ona mask (reticle) M is transferred to each of shot areas on the wafer Wby using the exposure apparatus of the embodiment described above (StepS44: exposure step). The wafer W for which the transfer has beencompleted is developed, i.e., the photoresist, to which the pattern hasbeen transferred, is developed (Step S46: development step). After that,the resist pattern, which is generated on the surface of the wafer W inaccordance with Step S46, is used as a mask to perform the processingincluding, for example, the etching with respect to the surface of thewafer W (Step S48: processing step).

The resist pattern herein refers to the photoresist layer formed withprotrusions and recesses having shapes corresponding to the patterntransferred by the exposure apparatus of the embodiment described above,wherein the recesses penetrate through the photoresist layer. In StepS48, the surface of the wafer W is processed via the resist pattern. Theprocessing, which is performed in Step S48, includes, for example, atleast one of the etching of the surface of the wafer W and the filmformation of a metal film or the like. In Step S44, the exposureapparatus of the embodiment described above transfers the pattern byusing, as the photosensitive substrate, the wafer W coated with thephotoresist.

In the embodiment described above, the present teaching is applied tothe exposure apparatus having the light source for supplying the EUVlight. However, there is no limitation to this. The present teaching isalso applicable to an exposure apparatus having a light source forsupplying light having any other wavelength than that of the EUV light.

In the embodiment described above, the present teaching is applied tothe illumination optical system of the EUV exposure apparatus using thereflection-type mask M. However, there is no limitation to this. Thepresent teaching is also applicable to an general illumination opticalsystem illuminating the first area based on the light from the lightsource.

According to the embodiments as described above, it is possible toilluminate the irradiation surface under a required illuminationcondition capable of achieving a high light efficiency while keeping theoccurrence of light loss at a low level. As a result, it is possible toachieve a high throughput.

The invention claimed is:
 1. An illumination optical system whichilluminates an illumination area on a first plane with a light from alight source, the illumination optical system comprising: a firstoptical system configured to irradiate the light from the light sourceonto a second plane such that the light has a cross sectional shape, onthe second plane, in which a first dimension in a first direction issmaller than a second dimension in a second direction crossing the firstdirection, the first direction optically corresponding to a shortdirection of the illumination area; and a second optical system whichincludes a plurality of reflection elements arranged on the secondplane, and which is configured to reflect the light from the firstoptical system, wherein the first optical system is configured to allowthe light to come into the second plane along a direction inclined, inthe first direction, relative to an axis crossing the second plane; andthe light exiting from the second optical system is inclined relative tothe light coming into the second optical system.
 2. The illuminationoptical system according to claim 1, wherein the light exiting from thesecond optical system is inclined, in a third direction opposite to thefirst direction, relative to the axis.
 3. The illumination opticalsystem according to claim 1, wherein a longitudinal direction of theillumination area crosses the first direction.
 4. The illuminationoptical system according to claim 1, wherein a width of the illuminationarea on the first plane in the short direction is smaller than a widthof the illumination area on the first plane in a direction crossing theshort direction.
 5. The illumination optical system according to claim4, wherein the illumination optical system is configured to illuminatethe illumination area along a direction inclined, in the shortdirection, relative to a normal line of the first plane.
 6. Theillumination optical system according to claim 1, further comprising athird optical system configured to reflect the light from the secondoptical system, wherein an optical path of the light travelling from thefirst optical system to the second optical system and an optical path ofthe light travelling from the second optical system to the third opticalsystem are positioned, in the first direction, differently from eachother.
 7. The illumination optical system according to claim 1, furthercomprising a third optical system which is arranged on a third directionside of an optical path of the light travelling from the first opticalsystem to the second optical system so as to reflect the light from thesecond optical system, the third direction being opposite to the firstdirection.
 8. The illumination optical system according to claim 1,wherein the second optical system is configured to reflect the lightfrom the first optical system such that the light reflected by thesecond optical system has a cross sectional shape, on a third plane,which has a third dimension in a third direction along the third planeand a fourth dimension in a fourth direction crossing the thirddirection, the third plane being defined so as to cross a travellingdirection of the light reflected by the second optical system on a sideof the second optical system at which the first plane is located, aratio of the fourth dimension with respect to the third dimension beinglarger than a ratio of the first dimension with respect to the seconddimension.
 9. The illumination optical system according to claim 1,wherein the light from the light source includes an EUV radiation. 10.The illumination optical system according to claim 1, wherein theillumination optical system is configured to form the illumination areaon a pattern surface of a reflection-type mask arranged on the firstplane.
 11. The illumination optical system according to claim 10,wherein the illumination optical system is configured to allow the lightto come into the illumination area along a direction inclined relativeto an axis orthogonal to the first plane.
 12. The illumination opticalsystem according to claim 11, wherein the light reflected by the patternsurface of the reflective-type mask is inclined relative to the axisorthogonal to the first plane.
 13. An exposure apparatus comprising: anillumination optical system as defined in claim 1 configured toilluminate a pattern surface arranged on the first plane; and aprojection optical system configured to project an image of the patternsurface onto a workpiece with a light from the pattern surface.
 14. Theexposure apparatus as defined in claim 13, wherein the workpiece isexposed by using the light source configured to supply an EUV radiation.15. An exposure method comprising: illuminating a pattern by using theillumination optical system as defined in claim 1; and exposing an imageof the pattern onto a workpiece.
 16. The exposure method according toclaim 15, wherein the illuminating of the pattern includes illuminatingthe pattern by using an EUV radiation.
 17. A method for producing adevice comprising: exposing a pattern onto a workpiece by using theexposure method as defined in claim 15; developing the workpiece onwhich the pattern has been transferred so as to form a mask layer whichhas a shape corresponding to the pattern on a surface of the workpiece;and processing the surface of the workpiece via the mask layer.